1. Field of Invention
This invention relates to natural ultra-violet absorbing compounds, and derivatives thereof, useful as broadly effective UVB/UVA-screening compounds for topical application to skin, and other surfaces where enhanced UV protection against the damaging effects of sunlight is desired.
2. Description of Prior Art Solar ultraviolet light is known to cause significant damage to human skin. Excessive exposure to solar UVB (i.e., wavelengths of the solar spectrum from 290 to 320 nm) causes erythema (sunburn), and chronic exposure can increase the risk of developing skin tumors. The UVA region of sunlight (i.e., wavelengths between 320 and 400 nm) penetrates more deeply into the skin than does UVB and was previously thought to have a minimal impact on the skin other than to promote tanning. However, UVA is now known to accelerate skin wrinkling and aging, negatively affect the immune system, and possibly increasing the risk of developing skin cancer. Thus significant effort has been devote toward finding effective means of protecting human skin and other materials from the damaging effects of both the UVB and UVA components of sunlight.
These efforts, by a great number of people, have resulted in the development and patenting of numerous synthetic organic compounds that absorb ultraviolet light, primarily UVB, to protect skin from the damaging effect of sunlight. Most commonly, mixtures of these UV-absorbing compounds are dispersed in lotions, creams, or sprays that are applied topically to the skin.
As early examples: U.S. Pat. No. 4,264,581 to Kerkhof et al. (1981) discloses a sunscreen composition containing a mixture of 2-ethythexyl dimethyl para-amino benzoate and 2-hydroxy-4-methoxy-benzophenone; U.S. Pat. No. 3,751,563 to Richardson (1973) discloses a sunscreen composition containing a mixture 2-ethoxyethyl para-methoxycinnimate, amyl para-dimethylamino benzoate, homo-menthyl salicylate, and 2-hydroxy4-methoxybenophenone; and U.S. Pat. No. 3,636,077 to Stauffer (1972) discloses a sunscreen composition containing salts of 5-benzoyl-4-hydroxy-2-methoxy benzene sulfonic acid and 4-aminobenzoic acids or esters. These pioneering compositions effectively absorbed UVB but have limited abilities to absorb in the UVA region of the solar spectrum.
More recently, efforts have focused on producing effective UVA blockers. One of the first patented UVA blockers to be included in sunscreens was 4-t-butyl4'-methoxydibenzoylmethane, also known as Octyl Methoxy Dibenzoyl Methane (CTFA), available from Givaudan Corporation under the trade name Parsol 1789. Since 1990, an increasing number of U.S. patents have been issued for novel UVA-absorbing compounds--examples include U.S. Pat. No. 5,210,275 to Sabatelli (1993), U.S. Pat. No. 5,298,647 to Robert et al. (1994), and U.S. Pat. No. 5,338,539 to Raspanti (1994).
Commonly, these synthetic compounds absorb most effectively in either the UVB or UVA region. Thus, for a sunscreen composition to be a broadly effective across the entire solar UV spectrum, it must contain a mixture of UVB-absorbing and UVA-absorbing compounds. Sabatelli et al. in U.S. Pat. No. 5,210,275 (1993) attempt to address this issue by synthesizing compounds containing both a UVB- and a UVA-absorbing chromophore. Alternatively, if a single chromophore had a very broad absorption band that was optimally situated within the solar UV spectrum, a compound containing such a chromophore could function as a broadly effective UVB/UVA screen.
Although nearly all UV-blocking compounds currently offered commercially in sunscreening compositions are synthetic materials, the patenting of naturally occurring UV-absorbing compounds is becoming more common. This interest in natural sunscreens is being driven, in part, by consumer preferences which are shifting away from synthetic materials and toward natural substances that can perform the same task with equal or greater efficiency. The diverse sources of novel, natural UV screens include, for example, terrestrial plants (U.S. Pat. No. 5,152,983 to Nambudiry et al. (1992)! and marine invertebrates (U.S. Pat. No. 5,352,793 to Bird et al. (1993)!. Several of these natural compounds, however, have significant limitations related to their stability and water solubility that prohibit their use in sunscreening compositions, and in particular "water-resistant" formulations.